Wall @ 5500rpm
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Teching In
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Wall @ 5500rpm I have a 355 in an 86 swb. I have the performer rpm cam and intake, world sportsman 2 heads, about 10 to 1 comp. 600cfm carb and stock mechanical pump, headers, 3 inch h-pipe, super 40s, built th-400, 373 posi 12 bolt. It pulls real hard to 5500 but you can hold it to the floor and it wont pass 5500. I'm thinking I maybe running outta fuel, but not sure. What do you guys think?
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Teching In
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It shouldnt be the valve springs. They are the standard that come on the heads. 1.25 diameter and good to .550 lift. It is a stock hei though, I thought you could get more out of those than 5500? It stumbles on the highway when the 4 barrels open, its like it coughs then goes. I'm thinking maybe rebuild the hei and step up the secondary jets on the carb?
Last edited by jh_shady01; Oct 27, 2009 at 06:11 PM.
Once again, what is the timing at? It will have the "cough" you talk about if the timing isnt right or there is a lean pocket from the carb not being tuned. If you dont know how to tune a car, you need someone to help you. It might run thrown together, but it will not be right till you are giving the engine what it wants.
if you are using a stock mechanical fuel pump, I would get a fuel pressure gauge to see what pressure you have up at 5000+ rpm at the carb inlet, mechanical pumps have a spring in them and I would imagine suffer the same problem as valve springs at a high enough rpm.
Also, a 600cfm carb (assuming it's an edelbrock) I'm not sure how well they do at high rpm compared to a holley (which are rated 650cfm) or if edelbrock's rating is conservative but at 5500 rpm for a 355 with 10:1 you're cfm requirements are very close to 600 cfm, so I would at least look into your airflow setup into the carb, make sure it's set up well, and of course that the carb is tuned correctly- correct metering rods and all that.
Also, a 600cfm carb (assuming it's an edelbrock) I'm not sure how well they do at high rpm compared to a holley (which are rated 650cfm) or if edelbrock's rating is conservative but at 5500 rpm for a 355 with 10:1 you're cfm requirements are very close to 600 cfm, so I would at least look into your airflow setup into the carb, make sure it's set up well, and of course that the carb is tuned correctly- correct metering rods and all that.
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I had the same problem on my old 2nd gen and it ended up being the carb. Just throwing some bigger weights in the distributor won't necessarily help. You need to set up a timing curve that works for your car.
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From: New Caney
ive ran a bone stock 50,000 mile mechanical pump on my truck and sprayed the hell out of it for ever... its still on there to this day and had no problem. the cough your running into is most likely untuned carb... loosen up the acc. pump bolt. ( the one in the front with the spring around it) loosen it up till the spring has just enough pressure on the bolt so it doesnt vibrate and make noise. do that and see if that takes care of the cough. if it doesnt step your jets in your primaries 3 to 4 sizes bigger. if your springs are good which just because they are new doesnt mean they are good, then the motor not pulling past 5500 should be the timing to low. set your timing at 32 degrees fully advanced and dont touch it again..
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From: New Caney
fully advanced as in when you go to set the timing unhook the vacuum advance and bring the motor's rpms up to 2800 to 3200 and set the timing then. that way when the weights in the dist are wide open your timing will be set at 32 degrees. no im not talking about the idle mixture screws. the acc. pump bolt it pushes the acc pump rod and in turn that sqeezes the acc pump itself. the looser that bolt is the quicker the fuel will be injected into the motor. thats what has always worked for me when i had a cough at the hit of WOT.
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From: New Caney
